Ferromagnetic tunnel junction element exhibiting high magnetoresistivity at finite voltage and tunnel magnetoresistive head provided therewith, magnetic head slider, and magnetic disk drive

ABSTRACT

A ferromagnetic tunnel junction element to produce a high ratio of magnetoresistance at finite voltages including the element operating voltage, and a device provided therewith such as tunnel magnetoresistive head, magnetic head slider, and magnetic disk drive. The ferromagnetic tunnel junction element has a laminate structure of ferromagnetic layer/metallic layer/insulating layer/metallic layer/ferromagnetic layer. (The metallic layer is one atom thick or two atoms thick.) The metallic layer and insulating layer have the crystalline regularity. The element is capable of detecting magnetism with its high magnetoresistivity, about three times that of conventional elements, at finite voltages. This element makes it possible to realize a highly sensitive magnetoresistive head. The magnetic head is used for the magnetic head slider which realizes a magnetic disk drive capable of reproducing magnetic information with high sensitivity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a ferromagnetic tunnel junctionelement to sense a magnetic field and relates also to a device providedtherewith such as tunnel magnetoresistive head, magnetic head slider,and magnetic disk drive.

[0003] 2. Description of the Related Art

[0004] High-density magnetic recording needs a sophisticated read head.This requirement is met by the magnetoresistive head based on giantmagnetoresistance effect (GMR effect), which has recently gainedcommercial acceptance. The current magnetoresistive head produces itsGMR effect through the spin valve film composed of ferromagnetic layer,non-magnetic metal layer, and ferromagnetic layer. The spin valve filmof this structure has a limited magnetoresistance ratio of about 10%.Hence, a more sensitive magnetoresistive element is required.

[0005] Researches to meet this requirement have recently revealed aphenomenon called ferromagnetic tunnel effect. This tunnel effectmanifests itself in the junction structure composed of ferromagneticlayer, amorphous insulating layer, and ferromagnetic layer, and itdepends on the relative angle of magnetization of the two ferromagneticlayers. (J. Magn. Mater. 139, L231 (1995); Phys. Rev. Lett. 74, 3273(1995)) Because of its ability to give a magnetoresistance ratio greaterthan 10% at room temperature, the above-mentioned phenomenon hasattracted keen attention on research and development for newmagnetoresistive elements. For its extremely high sensitivity tomagnetic field, the ferromagnetic tunnel effect film is greatly expectedto find use as a read head for ultra-high-density magnetic recordingexceeding 100 Gbit/inch².

[0006] The ferromagnetic tunnel effect had been analyzed by Julliere'stheory (Phys. Lett. A54, 252 (1975)), which is useful particularly forthe system containing an amorphous insulating layer. This theory definesthe spin polarization as P=(D↑−D↓)/(D↑+D↓), where D↑ and D↓ denoterespectively the density of state (or the number of states per unitenergy) of up-spin and down-spin in the ferromagnetic layer at Fermilevel. The value of P is used to represent the magnetoresistance ratioat zero voltage as follows.

TMR=100×2P ²/(1−P ²) [%]

[0007] The foregoing expression indicates that the larger the value ofP, the higher the magnetoresistance ratio. This idea has stimulated theresearch on the tunnel junction with La_(0.7)Sr_(0.3)MnO₃ which is ahalf-metallic ferromagnetic substance having P=1 at the absolute zero(Phys. Rev. Lett.,82,4288(1999)) This half-metallic ferromagneticsubstance is regarded as an effective spin injector in view of the factthat only up-spin electrons contribute to conduction. This substance isunder the stage of basic research and its practical application is beingpursued.

OBJECT AND SUMMARY OF THE INVENTION

[0008] The current tunnel magnetoresistive element represented byCo/Al—O/Co involves several problems in its practical use. The mostserious among them is that the magnetoresistivity steeply decreases withincreasing voltage. In other words, at the element's operating voltageof 0.2-0.4V, the magnetoresistivity decreases by more than half fromthat at zero voltage. Moreover, Julliere's expression suggests that theCo/Al—O/Co having an amorphous insulating layer would hardly give amagnetoresistivity higher than 40%.

[0009] On the other hand, it has been found that La_(0.7)Sr_(0.3)MnO₃ asa spin injector does not work at room temperature because the terminallayer most contributive to conduction has a Curie temperature as low asabout 180 K. Another problem is difficulty in film formation. Underthese circumstance, it is an urgent issue to develop a new material or anew film construction.

[0010] Accordingly, it is an object of the present invention to providea ferromagnetic tunnel junction element with film structure exhibitinghigh magnetoresistivity at finite voltage (including the elementoperating temperature) and devices provided therewith such as tunnelmagnetoresistive head, magnetic head slider, and magnetic disk drive.

[0011] The present invention is directed to a ferromagnetic tunneljunction element of the type having a tunnel insulating layer and afirst and second ferromagnetic layers arranged on both sides of saidtunnel insulating layer, wherein said tunnel insulating layer is inindirect contact with said first and second ferromagnetic layers with anoble metal layer interposed between them.

[0012] The ferromagnetic tunnel junction element mentioned above hassaid noble metal layer in the form of single crystal of noble metalatoms or in the form of monoatomic layer or diatomic layer of noblemetal atoms.

[0013] The ferromagnetic tunnel junction element mentioned above hassaid noble metal layer which contains any element of Au, Ag, and Cu.

[0014] The present invention is directed also to a magnetic disk driveof the type having a magnetic recording medium, a spindle motor torotate said magnetic recording medium, a magnetic head which is somounted on a slider as to perform information recording and reproducingon said magnetic recording medium, and an actuator to move said magnetichead to a desired position on the magnetic recording disk, wherein saidmagnetic head is provided with a ferromagnetic tunnel junction elementand a power source to supply electric current thereto, saidferromagnetic tunnel junction element having a tunnel insulating layerand a first and second ferromagnetic layers arranged on both sidesthereof, said tunnel insulating layer being in indirect contact withsaid first and second ferromagnetic layers with a noble metal layerinterposed between them.

[0015] It is another object of the present invention to provide amagnetic disk drive of the type having a magnetic recording medium, aspindle motor to rotate said magnetic recording medium, a magnetic headwhich is so mounted on a slider as to perform information recording andreproducing on said magnetic recording medium, and an actuator to movesaid magnetic head to a desired position on the magnetic recording disk,wherein said magnetic head is provided with a ferromagnetic tunneljunction element and a power source to supply electric current thereto,said ferromagnetic tunnel junction element having a tunnel insulatinglayer and a first and second ferromagnetic layers arranged on both sidesthereof, said tunnel insulating layer being in indirect contact withsaid first and second ferromagnetic layers with a noble metal layerinterposed between them.

[0016] In the aforesaid magnetic disk drive, said first and secondferromagnetic layers contain Co or Co_(x)Fe_(1-x) (x=0.7-1.0), and theaforesaid magnetic disk drive has a means to control the drive voltageapplied to said ferromagnetic tunnel junction element above 0.01 V andbelow 0.1 V.

[0017] In the aforesaid magnetic disk drive, said first and secondferromagnetic layers contain Co or Co_(x)Fe_(1-x) (x=0.7-1.0), and theaforesaid magnetic disk drive has a means to control the drive voltageapplied to said ferromagnetic tunnel junction element above 0.2 V andbelow 0.5 V.

[0018] In the aforesaid magnetic disk drive, said first and secondferromagnetic layers contain Fe, and the aforesaid magnetic disk drivehas a means to control the drive voltage applied to said ferromagnetictunnel junction element above 0.01 V and below 0.15 V.

[0019] In the aforesaid magnetic disk drive, said first and secondferromagnetic layers contain Fe, and the aforesaid magnetic disk drivehas a means to control the drive voltage applied to said ferromagnetictunnel junction element above 0.3 V and below 0.7 V.

[0020] In the aforesaid magnetic disk drive, said first and secondferromagnetic layers contain Ni_(x)Fe_(1-x) (x=0.7-1.0) and theaforesaid magnetic disk drive has a means to control the drive voltageapplied to said ferromagnetic tunnel junction element above 0.03 V andbelow 0.06 V.

[0021] Other and further objects, features and advantages of theinvention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic diagram showing the constitution of theferromagnetic tunnel junction element pertaining to the presentinvention;

[0023]FIG. 2 is a diagram showing the arrangement of atoms which is amodel of the ferromagnetic tunnel junction element pertaining to thepresent invention;

[0024]FIG. 3 is a schematic diagram showing atoms having the s-orbitalor d-orbital. “t” denotes the transfer integral, and “E” denotes siteenergy;

[0025]FIG. 4 is a schematic diagram showing the density of state ofd-orbitals in the ferromagnetic layer;

[0026]FIG. 5 is a diagram showing the density of state in the case wherethe ferromagnetic layer and the metallic layer are independent from eachother (above) and the density of state in the case where theferromagnetic layer and the metallic layer have joined together (below);

[0027]FIG. 6A is a diagram showing the density of state of the first andsecond metallic layers and the barrier of the insulating layer in theferromagnetic tunnel junction element of the present invention. Theenergy region of electrons contributing to tunneling conduction isindicated by a dotted zone. The thick small bar (−) in the figurerepresents the state which has a certain wave number vector k*;

[0028]FIG. 6B is a diagram showing the density of state (single peak)with the wave number vector k* of the first metallic layer, the barrierof the insulating layer, and the density of state (single peak) with thewave number vector k* of the second metallic layer, in the ferromagnetictunnel junction element of the present invention;

[0029]FIG. 7A is a diagram showing the current-voltage characteristicsof the ferromagnetic tunnel junction element of the present invention,in which the ferromagnetic layer is formed from Co or Co_(x)Fe_(1-x)(x=0.8-1.0) and the metallic layer is one atom thick;

[0030]FIG. 7B is a diagram showing the magnetoresistivity-voltagecharacteristics of the ferromagnetic tunnel junction element of thepresent invention, in which the ferromagnetic layer is formed from Co orCo_(x)Fe_(1-x) (x=0.8-1.0) and the metallic layer is one atom thick.Incidentally, the dotted line represents the magnetoresistivity-voltagecharacteristics in the absence of the metallic layer;

[0031]FIG. 8A is a diagram showing the current-voltage characteristicsof the ferromagnetic tunnel junction element of the present invention,in which the ferromagnetic layer is formed from Co or Co_(x)Fe_(1-x)(x=0.8-1.0) and the metallic layer is two atoms thick;

[0032]FIG. 8B is a diagram showing the magnetoresistivity-voltagecharacteristics of the ferromagnetic tunnel junction element of thepresent invention, in which the ferromagnetic layer is formed from Co orCo_(x)Fe_(1-x) (x=0.8-1.0) and the metallic layer is two atoms thick;

[0033]FIG. 9A is a diagram showing the current-voltage characteristicsof the ferromagnetic tunnel junction element of the present invention,in which the ferromagnetic layer is formed from Ni_(x)Fe_(1-x)(x=0.8-1.0) and the metallic layer is one atom thick;

[0034]FIG. 9B is a diagram showing the magnetoresistivity-voltagecharacteristics of the ferromagnetic tunnel junction element of thepresent invention, in which the ferromagnetic layer is formed fromNi_(x)Fe_(1-x) (x=0.8-1.0) and the metallic layer is one atom thick;

[0035]FIG. 10A is a diagram showing the current-voltage characteristicsof the ferromagnetic tunnel junction element of the present invention,in which the ferromagnetic layer is formed from Ni_(x)Fe_(1-x)(x=0.8-1.0) and the metallic layer is two atoms thick;

[0036]FIG. 10B is a diagram showing the magnetoresistivity-voltagecharacteristics of the ferromagnetic tunnel junction element of thepresent invention, in which the ferromagnetic layer is formed fromNi_(x)Fe_(1-x) (x=0.8-1.0) and the metallic layer is two atoms thick;

[0037]FIG. 11A is a diagram showing the current-voltage characteristicsof the ferromagnetic tunnel junction element of the present invention,in which the ferromagnetic layer is formed from Fe and the metalliclayer is one atom thick;

[0038]FIG. 11B is a diagram showing the magnetoresistivity-voltagecharacteristics of the ferromagnetic tunnel junction element of thepresent invention, in which the ferromagnetic layer is formed from Feand the metallic layer is one atom thick;

[0039]FIG. 12A is a diagram showing the current-voltage characteristicsof the ferromagnetic tunnel junction element of the present invention,in which the ferromagnetic layer is formed from Fe and the metalliclayer is two atoms thick;

[0040]FIG. 12B is a diagram showing the magnetoresistivity-voltagecharacteristics of the ferromagnetic tunnel junction element of thepresent invention, in which the ferromagnetic layer is formed from Feand the metallic layer is two atoms thick;

[0041]FIG. 13 is a schematic diagram showing the magnetic head of thepresent invention;

[0042]FIG. 14 is a schematic diagram showing the magnetic disk drivecontaining the magnetic head slider of the present invention; and

[0043]FIG. 15 is a schematic diagram showing the magnetic disk drive ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Solution to the above-mentioned problems needs a new layerconstruction in place of the conventional layer construction such asCo/Al—O/Co containing an amorphous insulating layer. Several models oflayer construction were examined for their characteristics by computersimulation based on the quantum theory.

[0045] The computer simulation describes the system in terms of thesingle-orbital tight binding model. The parameters for this model isevaluated based on the result of calculations of the first principleelectron state. Moreover, the value of current at the absolute zero iscalculated by applying to this model the method of Keldysh-GreenFunction (J. Phys. C: Solid St. Phys. 4, 916 (1971)).

[0046] The result of the computer simulation has suggested that theabove-mentioned problem is solved with the ferromagnetic tunnel junctionelement which is composed of a first ferromagnetic layer and a secondferromagnetic layer which face each other with an insulating layerinterposed between them, said first and second ferromagnetic layersbeing in indirect contact with said insulating layer, with a metalliclayer interposed between them, said metallic layer being a monoatomiclayer or diatomic layer of any of Au, Ag, and Cu having conductionelectrons, said metallic layer and said insulating layer havingcrystalline regularity. In addition, the object of the present inventionis achieved with those devices which are provided with the ferromagnetictunnel junction element, such as magnetic head, head slider, andmagnetic disk drive.

[0047] The examples of the present invention will be described in moredetail with reference to the accompanying drawings.

EXAMPLE 1

[0048]FIG. 1 is a schematic diagram showing the magnetic sensing devicepertaining to the present invention. The magnetic sensing device iscomposed of a first ferromagnetic layer 1, a first metallic layer 4, aninsulating layer 3, a second metallic layer 5, and a secondferromagnetic layer 2, which are sequentially laminated one overanother. It also has a constant-voltage power supply 6. The first andsecond metallic layers are monoatomic layers or diatomic layers, and themetallic layers and the insulating layer have crystalline regularity.The second ferromagnetic layer 2 magnetizes freely in any direction inresponse to external magnetic fields (not shown). Thus, the electricresistance in the direction perpendicular to the film plane changes inproportion to the angle of rotation, and this change in resistancemanifests itself as the magnetoresistive effect, which is expressed interms of the difference between P (parallel) and AP (antiparallel) asexplained in detail below.

[0049] The computer simulation for the tunnel magnetoresistive materialemploys (1) the tight binding model and (2) the method of Keldysh-GreenFunction. For (1), refer to “Jisei no Riron” (Theory of Magnetism) by T.Nagamiya, from Yoshioka Bookstore; “Kotai-Kozou to Bussei”(Solids—Structure and Characteristics) by J. Kanamori et al. fromIwanami Bookstore; and “Jisei” (Magnetism) by K. Yoshida, from IwanamiBookstore. For (2), refer to J. Phys. C: Solid St. Phys. 4, 916 (1971).First, the tunnel junction system will be described in terms of thetight binding model. Then, the method of Keldysh-Green Function will beapplied to the system to investigate the electrical conductivity.

[0050] (1) Explanation of the Tight Binding Model

[0051] Let us consider a system consisting of atoms arranged in theactual (two-dimensional) space as shown in FIG. 2. Each atom inherentlyhas a plurality of orbitals (s-orbital, p-orbital, d-orbital, and so on)which differ in orbital angular momentum. Some orbitals greatlycontribute to the magnetoresistive effect, but others do not. In thisdiscussion, consideration is given only to those orbitals which greatlycontribute to the magnetoresistive effect. Thus, the ferromagneticlayer, metallic layer, and insulating layer are described respectivelyin terms of d-orbital, s-orbital, and s-orbital. In other words, it isassumed that each atom has a single orbital. In this case, the parameterrepresenting individual atoms includes site energy (energy E ofelectrons on the orbit) and transfer integral (t) (magnitude of energyrequired for transfer from one site to the other). The transfer integral(t) has the dimension of energy. See FIG. 3.

[0052] The two-dimensional energy expression (dispersion relation) shownin FIG. 3 may be written as follows by using the parameters.E(k) = E − 2t[cos (k × c) + cos (k × c)]

[0053] where, k [=(kx, ky)] denotes the two-dimensional wave numbervector (it is related with momentum P by P=ηk, where η is Planckconstant divided by 2π), and c denotes the lattice constant. Moreover,this energy expression gives the density of states, which represents thenumber of states per unit energy. The density of states is defined asfollows, in which ε denotes an arbitrary energy.

D(ε)=Σk D(ε,k)/Σk l

D(ε,k)=δ(ε−E(k))

[0054] where, Σk denotes the sum over k in the first Brillouin zone(Kittel, Introduction to Solid State Physics).

[0055] Now, let us pay attention only to d-orbital in the ferromagneticlayer. When atoms having d-orbital are arranged in three-dimensionalspace, they assume the density of state in one layer as schematicallyshown in FIG. 4. The center of the density of state of up-spin anddown-spin correspond respectively to the site energies E↑ and E↓, andthe width of the density of state is related with the transfer integralt. Incidentally, E_(F) stands for the Fermi level, which represents themaximum energy level when all states above the ground state are occupiedby electrons.

[0056] The following is an explanation of the site energy Es (s=↑ or ↓)and the transfer integral t. The site energy E_(S) is approximated asfollows.

E _(S) =E _(para)−_(s) U<M _(i)>/2

E _(para) =E ₀ +U<N _(i)>/2E₀ = ∫_(allspace)r₁φ * (r₁ − R_(i))[−h²∇1²/2m + (−Z_(i)e²)|r₁ − R_(i)|+∑_(ℶ)(−Z_(j)e²)/|r₁ − R_(ℶ)|]φ(r₁ − R_(i))U = ∫∫_(allspace)r₁r₂φ * (r₁ − R_(i))φ * (r₂ − R_(i))[e²/|r₁ − r₂|])φ(r₂ − R_(i))

[0057] where, φ(r₂−R_(i)) denotes the orbital function of electron 1 inthe atom at R_(i); m denotes the mass of an electron; −e denotes thecharge of an electron; +Z_(i)e denotes the charge of an ion at R_(i);<M_(i)>denotes the magnetization at R_(i); <N_(i)> denotes the number ofelectrons at R_(i); U denotes the Coulomb interaction between electrons;E_(s) denotes the total energy which electrons bound by ions feel;E_(para) denotes the paramagnetic potential; and E₀ (the first term ofE_(para)) includes kinetic energy (first term), potential due to ions atR_(i) (second term), and potential due to surrounding ions (third term).The difference in site energy between up-spin and down-spin is calledexchange splitting energy, and it originates from _(S)U<M_(i)>/2including Coulomb mutual action U between electrons. Incidentally, theterm containing U should be considered for d-orbital, because d-orbitaltends to localize in ions and have a large value of U. In the following,A denotes the exchange splitting energy.

[0058] The transfer integral t is represented as follows.t = ∫_(allspace)r  φ * (r − R_(i))[Σ_(k( ≠ 1))(−Z_(k)e²)/|r₁ − R_(k)|]φ(r₁ − R_(i))

[0059] It represents the transfer energy of electrons between R_(i) andR_(j) due to the mutual action of electrons with surrounding ions.

[0060] The above-mentioned site energy E_(S), the transfer integral t,and the Fermi level E_(F) can be evaluated based on the result ofcalculations of the first principle electron state. In the presentinvention, their values were determined with reference to the followingliterature.

[0061] Harrison, Solid State Table of the Elements in ElectronicStructure and the Properties of Solids (W. H. Freeman & Co., SanFrancisco, (1980))

[0062] J. Phys. Soc. Jpn. 60 376(1991)

[0063] Phys. Rev. B54 15314(1996)

[0064] The density of state is schematically shown in FIG. 5 ford-orbital of the ferromagnetic layer and s-orbital of the metal layerbased on the above-mentioned literature. It is noted from the figurethat the metallic layer alone is originally non-magnetic and hence theexchange splitting does not exist between the up-spin state and thedown-spin state. However, the metallic layer brings about exchangesplitting upon combination with the ferromagnetic layer. In thefollowing, Δm denotes the exchange splitting energy of the metalliclayer.

[0065] The density of state of the end layer (adjacent to the insulatinglayer) of the metallic layer is included in the expression (given later)for current in the tunnel junction system. It is known that the metalliclayer plays an important role in tunneling conduction. The differencebetween the number of majority electrons (the density of state) and thenumber of minority electrons (the density of state) in the metalliclayer which originates from the exchange splitting plays an importantrole in the magnetoresistive effect.

[0066] (2) Explanation of the Method of Keldysh-Green Function (J. Phys.C: Solid St. Phys. 4, 916 (1971))

[0067] As compared with the resistivity of the insulating layer, that ofother layers is negligibly small. Therefore, it is considered that thefirst ferromagnetic layer and the first metallic layer at the samepotential and the second ferromagnetic layer and the second metalliclayer are at the same potential, and only the insulting layer, which hasa large resistivity, varies in voltage in the film thickness directiondue to the surface charge of the metallic layer. In other words, onlythe barrier of the insulating layer varies in voltage in the filmthickness direction. FIG. 6A is a schematic diagram showing the densityof state of the first and second metallic layers and the barrier of theinsulating layer which were obtained from the above-mentioned tightbinding model. The energy region of electrons contributing to tunnelingconduction is indicated by a dotted zone. Incidentally, this schematicdiagram shows only those parts necessary for the subsequent explanation,with the first and second ferromagnetic layers being omitted.

[0068] The value of current at the absolute zero by the method ofKeldysh-Green Function is expressed as follows when electrons pass fromthe first ferromagnetic layer to the second ferromagnetic layer whilekeeping their spin direction. $\begin{matrix}{{I_{s}(V)} = {\int_{E_{F - V}}^{E_{F}}\quad {{{ɛ\Gamma}_{S}\left( {ɛ,\quad V} \right)}}}} \\{{\Gamma_{S}\left( {ɛ,\quad V} \right)} = \left. \Sigma_{k} \middle| {T_{S}\left( {ɛ,\quad V,\quad k} \middle| {}_{2}\quad {{D_{L,\quad S}\left( {ɛ,\quad V,\quad k} \right)}{D_{R,\quad S}\left( {ɛ,\quad k} \right)}} \right.} \right.}\end{matrix}$

[0069] where, s denotes spin (s=↑ or ↓), |T_(S)(ε,V,k|² denotes thetransmission coefficient, D_(L,S)(ε,V,k) denotes the density of state ofthe end layer (adjacent to the insulating layer) of the first metalliclayer 4 having an energy (e) and the dependence on the wave vector k,and D_(R,S)(ε,k) denotes the density of state of the end layer (adjacentto the insulating layer) of the first metallic layer 5 having an energy(e) and the dependence on the wave vector k. The integral expresses thatelectrons in the range from EF-V to EF contribute to tunnelingconduction. What is important is that the conductance is summed over kbecause k is conserved in the layer for the system with crystallineregularity. This is a big difference from the conventional system withan amorphous insulating layer in whichΓ_(S)(ε,V)∝D_(L,S)(ε,V)D_(R,S)(ε), whereD_(L,S)(ε,V)=ΣkD_(L,S)(ε,V,k)/Σk1 and D_(R,S)(ε)=ΣkD_(R,S)(ε,k)/Σk1.

[0070] Then, the magnetic resistivity is defined as follows toinvestigate the magnetoresistive effect.TMR = 100 × [I_(P)(V) − I_(AP)(V)]/I_(P)(V)  [%]

[0071] where, the current value is a sum of the current value due toup-spin and the current value due to down-spin. I_(AP) representsparallel (anti-parallel) magnetization arrangement

[0072] The present inventors are the first to apply the above-mentionedmethod to real substances. They have demonstrated the possibility ofrealizing a highly sensitive magnetoresistive element by investigatingindividual substances based on the results of computer simulation.

[0073] This example presents a sample consisting of a firstferromagnetic layer 1 of Co or Co_(x)Fe_(1-x) (x=0.8-1.0), a firstmetallic layer 4 of Cu, an insulating layer 3 of Al—O, a second metalliclayer 5 of Cu, and a second ferromagnetic layer 2 of Co orCo_(x)Fe_(1-x) (x=0.8-1.0). The first and second ferromagnetic layers 1and 2 are 500 atoms thick. The first and second metallic layers 4 and 5are one or two atoms thick. The insulating layer 3 is five atoms thick.All the layers have the crystal structure of simple cubic lattice.

[0074] The parameters for the tight binding model were determined asfollows on the basis of the above-mentioned literature (Harrison,Electronic Structure and the Properties of Solids; J. Phys. Soc. Jpn. 60(1991) 376; and Phys. Rev. B54 (1996). 15314

E↑−E _(Cu)=−2.5 eV, E↓−E _(Cu)=−1.5 eV, E _(Al—O) −E _(Cu)=80 eV, and E_(F) −E _(Cu)=−1.0 eV

[0075] where, E↑ and E↓ each denote the site energy of up-spin anddown-spin of d-orbital of Co or Co_(x)Fe_(1-x) (x=0.8-1.0); E_(Cu)denotes the energy of s-orbital of Cu; and E_(Al—O) denotes the centerof the conduction band of Al—O. Incidentally, the transfer integral wascarried out assuming t=1.0 eV for all the substances in consideration ofthe width of the density of state.

[0076] For the ferromagnetic layer of Co or Co_(x)Fe_(1-x) (x=0.8-1.0),A 1.0 eV. For the metallic layer one atom thick on Co or Co_(x)Fe_(1-x)(x=0.8-1.0), Δm≈0.3 eV. The Am can be obtained from the difference inenergy level between the up-spin state and down-spin state for k in thestate of k having an energy in the vicinity of Fermi level.

[0077]FIG. 7A shows how current depends on voltage. In the voltage rangefrom V=0.2 to V=0.5, the current value of up-spin for the anti-parallelmagnetization arrangement has a peak.

[0078] The mechanism for this peak is explained in the following. First,the center energy of the density of state of the metallic layer isobtained at a voltage V. By using the site energy E↑ and E↓ for up-spinstate and down-spin state at zero voltage, the up-spin state ofanti-parallel magnetization arrangement at a voltage V is E↑+V for thefirst metallic layer and E↓ for the second metallic layer. See FIG. 7A.It is to be noted that E↓ for the second metallic layer becomes the siteenergy of up-spin due to the anti-parallel magnetization arrangement. Inthe case where the first and second metallic layers are equal in energy,that is,

E↑+V=E↓

[0079] up-spin electrons in antiparallel magnetization arrangement arein such a state that the state with a certain wave number vector k* ofthe first metallic layer and the state with the same wave number vectork* of the second metallic layer have an approximately equal energy. SeeFIG. 6A. This condition makes electrons in up-spin state to transmiteasily. (By contrast, electrons in down-spin state go away.) This isapparent from the fact that the density of state D_(s)(E,k) at each khas the single peak for the energy corresponding to the k (see FIG. 6B)and the current value increases when the peaks of the first and secondmetal layers have an equal energy (see the above-mentioned expressionfor current). On the other hand, in the case of parallel magnetizationarrangement with up-spin and down-spin, the state for k* in the firstmetallic layer does not coincide with the state for k* in the secondmetallic layer but they tend to go away from each other. This conditionmakes it difficult for electrons to transmit. Incidentally, theabove-mentioned expression may be written as V=E↓−E↑; this correspondsto an instance in which voltage is equal to the exchange splittingenergy of the metallic layer. In fact, the peak position obtainedcoincides approximately with the above-mentioned exchange splittingenergy Am (=0.3 eV). That is, this condition permits only thoseelectrons in the antiparallel up-spin state to transmit easily.

[0080] As the voltage dependence of magnetoresistivity (in FIG. 7B)shows, the magnetoresistivity has the maximum value of 80% in the regionfrom 0.2 V to 0.5 V. This magnitude is about three times larger thanthat in the case where the metallic layer does not exist (represented bythe dotted line in FIG. 7B). Also, this system gives themagnetoresistivity higher than 70% even in the region from 0.01 V to 0.1V. Thus, the magnetoresistive element in this example exhibits highsensitivity in the region from 0.2 V to 0.5 V and from 0.01 V to 0.1 V.

[0081] The computer simulation was carried out also in the case wherethe metallic layer is two atoms thick. In the end layer of the metalliclayer on Co or Co_(x)Fe_(1-x) (x=0.8-1.0), the exchange splitting energyis Δm≈0.09 eV. The results are shown in FIG. 8.

[0082] The current value due to up-spin for anti-parallel magnetizationarrangement has a peak in the voltage region from 0.07 V to 0.12 V. (SeeFIG. 8A.) In this voltage region, the magnetoresistivity has valueslarger than 70%. (See FIG. 8B.) Moreover, magnetoresistivity greaterthan 70% is obtained even in the region from 0.01 V to 0.03 V. Thus, themagnetoresistive element in this example exhibits high sensitivity inthe region from 0.07 V to 0.12 V and from 0.01 V to 0.03 V.

[0083] The same investigation as above was conducted on samples in whichthe metallic layer is made of Ag or Au. Similar results as above wereobtained because the parameters for Ag and Au are almost the same asthose for Cu. Thus, the magnetoresistive element in this example alsoexhibits high sensitivity in the region from 0.07 V to 0.12 V and from0.01 V to 0.03 V. Incidentally, the above-mentioned characteristics aremaintained even at room temperature because Co or Co_(x)Fe_(1-x)(x=0.8-1.0) has a Curie temperature higher than 1000 K.

EXAMPLE 2

[0084] The same computer simulation as in Example 1 was performed onsamples in which the ferromagnetic layer is made of Ni_(x)Fe_(1-x)(x=0.8-1.0) and the metallic layer is made of Ag, Au, or Cu and is oneatom thick.

[0085] The parameters were set up as follows on the basis of theliterature mentioned in Example 1.

E↑−E _(m)=−2.25 eV, E↓−E _(m)=−1.75 eV, E _(Al—O) −E _(m)=8.0 eV, and E_(F) −E _(m)=−1.0 eV.

[0086] where, E↑ and E↓ are respectively the site energy of up-spin anddown-spin of d-orbital of Ni_(x)Fe_(1-x) (x=0.8-1.0); E_(m) is theenergy of s-orbital of Cu, Ag, and Au; and E_(Al—O) denotes the centerof the conduction band of the insulating layer of Al—O. Incidentally,the transfer integral was carried out assuming t=1.0 eV for all thesubstances in consideration of the width of the density of state.

[0087] The exchange splitting energy is Δm≈0.12 eV at the end layer ofthe metallic layer on Ni_(x)Fe_(1-x) (x=0.8-1.0).

[0088] The current value due to up-spin for anti-parallel magnetizationarrangement has a peak in the voltage region from 0.1 V to 0.3 V. (SeeFIG. 9A.) In this voltage region, the magnetoresistivity has valueslarger than 70%. (See FIG. 9B.) Moreover, magnetoresistivity greaterthan 70% is obtained even in the region from 0.01 V to 0.05 V. Thus, themagnetoresistive element in this example exhibits high sensitivity inthe region from 0.1 V to 0.3 V and from 0.01 V to 0.05 V.

[0089] The computer simulation was carried out also in the case wherethe metallic layer of Ag, Au, or Cu is two atoms thick. In the end layerof the metallic layer on Ni_(x)Fe_(1-x) (x=0.8-1.0), the exchangesplitting energy is Δm≈0.09 eV.

[0090] The current value due to up-spin for anti-parallel magnetizationarrangement has a peak in the voltage region from 0.03 V to 0.06 V. (SeeFIG. 10A.) In this voltage region, the magnetoresistivity has valueslarger than 70%. (See FIG. 10B.) Thus, the magnetoresistive element inthis example exhibits high sensitivity in the region from 0.03 V to 0.06V.

[0091] Incidentally, the above-mentioned characteristics are maintainedeven at room temperature because Ni_(x)Fe_(1-x) (x=0.8-1.0) has a Curietemperature higher than 600 K.

EXAMPLE 3

[0092] The same computer simulation as in Example 1 was performed onsamples in which the ferromagnetic layer is made of Fe and the metalliclayer is made of Ag, Au, or Cu and is one atom thick.

[0093] The parameters were set up as follows on the basis of theliterature mentioned in Example 1.

E↑−E _(m)=−2.75 eV, E↓−E _(m)=−1.25 eV, E _(Al—O) −E _(m)=8.0 eV, and E_(F) −E _(m)=−1.0 eV.

[0094] where, E↑ and E↓ are respectively the site energy of up-spin anddown-spin of d-orbitals of Fe; E_(m) is the energy of s-orbitals of Cu,Ag, and Au; and E_(Al—O) denotes the center of the conduction band ofthe insulating layer of Al—O. Incidentally, the transfer integral wascarried out assuming t=1.0 eV for all the substances in consideration ofthe width of the density of state.

[0095] The exchange splitting energy is Δm≈0.55 eV in the end layer ofthe metallic layer on Fe.

[0096] The current value due to up-spin for anti-parallel magnetizationarrangement has a peak in the voltage region from 0.3 V to 0.7 V. (SeeFIG. 11A.) In this voltage region, the magnetoresistivity has valueslarger than 70%. (See FIG. 11B.) Moreover, magnetoresistivity greaterthan 70% is obtained even in the region from 0.01 V to 0.15 V. Thus, themagnetoresistive element in this example exhibits high sensitivity inthe region from 0.3 V to 0.7 V and from 0.01 V to 0.15 V.

[0097] The computer simulation was carried out also in the case wherethe metallic layer of Ag, Au, or Cu is two atoms thick. In the end layerof the metallic layer on Fe, the exchange splitting energy is Δm≈0.14eV.

[0098] The current value due to up-spin for anti-parallel magnetizationarrangement has a peak in the voltage region from 0.1 V to 0.2 V. (SeeFIG. 12A.) In this voltage region, the magnetoresistivity has valueslarger than 70%. (See FIG. 12B.) Thus, the magnetoresistive element inthis example exhibits high sensitivity in the region from 0.1 V to 0.2 Vand from 0.01 V to 0.05 V.

[0099] Incidentally, the above-mentioned characteristics are maintainedeven at room temperature because Fe has a Curie temperature higher than1000 K.

EXAMPLE 4

[0100]FIG. 13 is a schematic diagram showing the magnetoresistive headprovided with the above-mentioned ferromagnetic tunnel junction element.The head consists of a substrate 75, a lower shield layer, an underlyinglayer, a ferromagnetic tunnel effect element (as the magnetoresistiveelement), an upper shield layer (functioning also as the lower core ofthe recording head), and an upper core for the recording head with arecording gap layer placed thereunder, which are formed sequentially ontop of the other. The ferromagnetic tunnel effect element (as themagnetoresistive element) is held between a pair of electrodes to applydriving current to the element. This structure realizes themagnetoresistive head which exhibits the high ratio of change inmagnetoresistance as mentioned in the foregoing examples.

Example 5

[0101]FIG. 14 is a schematic diagram showing the magnetic disk drivecontaining the magnetic head slider 60 which is provided with themagnetoresistive head of the present invention. The slider 60 has themagnetoresistive head provided with the magnetoresistive head of thepresent invention, a pair of electrodes, and terminals 65 to supplycurrent to the electrodes. This magnetic slider exhibits the high ratioof change in magnetoresistance as mentioned in the foregoing examples.

Example 6

[0102]FIG. 15 is a schematic diagram showing the magnetic disk drivewhich is provided with the magnetic head slider of the presentinvention. The magnetic head slider 55 is equipped with theferromagnetic tunnel effect element of the present invention. Themagnetic disk drive has a power supply 64 (see the power supply 6 inFIG. 1) to supply current to the ferromagnetic tunnel effect element.This structure realizes the magnetic disk drive with high-sensitivereproducing characteristics owing to the high ratio of change inmagnetoresistance as mentioned in the foregoing examples.

[0103] The ferromagnetic tunnel junction element of the presentinvention has a laminate structure of ferromagnetic layer/metalliclayer/insulating layer/metallic layer/ferromagnetic layer. (The metalliclayer is one atom thick or two atoms thick.) The metallic layer andinsulating layer have the crystalline regularity. The element is capableof detecting magnetism with its high magnetoresistivity, about threetimes that of conventional elements, at finite voltages. This elementmakes it possible to realize a highly sensitive magnetoresistive head.The magnetic head is used for the magnetic head slider which realizes amagnetic disk drive capable of reproducing magnetic information withhigh sensitivity.

[0104] The foregoing invention has been described in terms of preferredembodiments. However, those skilled, in the art will recognize that manyvariations of such embodiments exist. Such variations are intended to bewithin the scope of the present invention and the appended claims.

What is claimed is:
 1. A ferromagnetic tunnel junction element of thetype having a tunnel insulating layer and a first and secondferromagnetic layers arranged on both sides of said tunnel insulatinglayer, wherein said tunnel insulating layer is in indirect contact withsaid first and second ferromagnetic layers with a noble metal layerinterposed between them.
 2. The ferromagnetic tunnel junction element asdefined in claim 1, wherein said noble metal layer is in the form ofsingle crystal.
 3. The ferromagnetic tunnel junction element as definedin claim 1, wherein said noble metal layer is in the form of monoatomiclayer or diatomic layer or their mixed layer composed of noble metalatoms.
 4. The ferromagnetic tunnel junction element as defined in claim1, wherein said noble metal layer contains any element of Au, Ag, andCu.
 5. The ferromagnetic tunnel junction element as defined in claim 1,wherein said tunnel insulating layer is formed from a crystallinematerial.
 6. A tunnel magnetoresistive head which comprises amagnetoresistive element, magnetic shield layers formed on both sides ofsaid magnetoresistive element, and a pair of electrode to apply drivecurrent to said magnetoresistive element, said magnetoresistive elementhaving a tunnel insulating layer, a first and second ferromagneticlayers arranged on both sides of said tunnel insulating layer, a noblemetal layer formed between said tunnel insulating layer and said firstferromagnetic layer, and a noble metal layer formed between said tunnelinsulating layer and said second ferromagnetic layer.
 7. A magnetic headslider which comprises a magnetoresistive element, magnetic shieldlayers formed on both sides of said magnetoresistive element, and a pairof electrode to apply drive current to said magnetoresistive element,said magnetoresistive element having a tunnel insulating layer, a firstand second ferromagnetic layers arranged on both sides of said tunnelinsulating layer, a noble metal layer formed between said tunnelinsulating layer and said first ferromagnetic layer, and a noble metallayer formed between said tunnel insulating layer and said secondferromagnetic layer, and terminals to apply current to said pair ofelectrodes.